In the following study the effective dose of kale-containing food was investigated in a randomized, double-blind, placebo-controlled, crossover trial (Kondo F, et.al., 2016).
The study included 42 participants between the age of 21 and 64 years with fasting plasma glucose levels of 125 mg/dl and lower. The participants consumed either a placebo or kale-containing food. 2 doses of kale were tested, a low dose of 7g or a high dose of 14g together with a high-carbohydrate meal. 30 and 120 minutes after the test meal intake, both blood glucose levels and insulin levels were checked.
The results showed that both the low and the high dose of kale significantly lowered the blood glucose levels.
You can add kale to both salads and soups, or you can add it to a vegetable shake, and according to this research you don’t need to add a lot to get benefits.
Sumio Kondo, Asahi Suzuki, Mihoko Kurokawa, Keiji Hasumi, Intake of kale suppresses postprandial increases in plasma glucose: A randomized, double-blind, placebo-controlled, crossover study, Biomed Rep. 2016 Nov;5(5):553-558.